The present invention resides in use of time domain multiplexing to effect the summation necessary for use of multiple references in a multi-reference amplifier.
Multi-reference amplifiers improve resolution available to the load by the summation of multiple voltages which are individually modulated. My co-pending U.S. patent application Ser. No. 09/831,595 shows use of a bridged-tied load output to perform continuous load summation to this end. In some applications, however, cost or other factors preclude the use of a bridged output stage. A need exists for a simple, more cost-effective output stage capable of multi-reference operation.
The filtered output of multiple possible voltage levels are AC-coupled to a load. An incoming data stream provides input to a pulsewidth modulator which issues control voltages to three or more switching devices, respectively. A first switching device provides a controlled connection to the incoming power supply (V+), a second switching device provides a controlled connection to a lower reference voltage (VR), and a third switching device provides a controlled connection to common, or ground. The common connection of switching devices provides an input to an inductor, which, in conjunction with a capacitor removes out-of-band components before presentation of the output to one side of load. Another capacitor provides a pseudo-ground for the second side of load in a manner consistent with the art of AC-coupled power amplifiers.